Today's incandescent lighting is only about 5% efficient, yet enjoys a dominant market share due to a very low cost. A need has arisen for a high efficacy, low cost, non-toxic, fixture compatible, high quality light source. Various technologies have attempted to fill this need, but all have failed in at least one way or another. For example, U.S. Pat. No. 6,768,256 “Photonic crystal light source” and U.S. Pat. No. 6,611,085 “Photonically engineered incandescent emitter” disclose a woodpile PBG, which is a 3D layer by layer structure. The thermally stimulated PBG emitter has a significant increase efficiency over a black-body emitter. But, this woodpile approach requires an expensive enhanced state-of-the-art semiconductor fab for manufacture, hardly suited to commodity lighting. U.S. Pat. No. 7,085,038 “Apparatus having a photonic crystal” disclosed an inverse opal PBG, which is a 3D colloidal structure. Although the colloidal method reduces the cost, it is still costly to manufacture and the quality of the opal is difficult to maintain using the methods disclosed.
Another PBG structure has been disclosed in Ivan Celanovic, David Perreault, and John Kasskian, “Resonant-cavity enhanced thermal emission”, Physical Review B 72,075 (2005), DOI: 10,1103/PhysRevB, 72,075127, Notably, this structure incorporates a 1D PBG structure, a thermal cavity, and a mirror. The PBG structure is composed of alternating layers of 0.17 μm thick silicon and 0.39 μm thick silicon dioxide. The thermal cavity, composed of a 0.78 μm thick silicon dioxide, is a defect in the PBG and increases the emissivity of the device. The mirror is composed of tungsten or silver. Results show quasi-monochromatic thermal emission in the IR and 2.4 μm and good directivity. Only planar structures are disclosed.
ThermoPhotoVoltaic (TPV) electric generation offers the potential to recover vast amounts of waste heat, yet has failed to operate at reasonable efficiency or have a reasonable cost. PBG emitters have been proposed to increase the spectral efficiency of the thermal emitter in the TPV system. Also, photonic heat pumps have not yet been commercially realized due to cost/performance issues. A need has arisen for a narrow band thermally driven focused light source.
Electronic displays suffer from high cost, low brightness, poor contrast, perceptive color aberrations due to edge effects color combining of red, green, and blue pixels, various effects of backlighting, and failure of a main light source. A need has arisen for low cost, emissive displays.
Temperature and strain sensors are frequently limited due to; size, operating environment, resolution due to few measuring points and sensor size, multiplexing a larger number of measurement points, or connectivity issues due to movement of the point to be measured, electrical noise, and number of connections. Thus a need has arisen for tiny, remotely readable, rugged sensors.
Although Photonic Band Gap (PBG) technologies hold promise in all of these applications, they have been severely limited due to the choice of the desired structure, the manufacturability of the structure, and the cost of making the structure.
Traditional black body emitters are essentially isotropic. The light pattern is essentially determined by the shape of the fixture or bulb.